Information By Segment (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Segment Reporting Information [Line Items]
Revenues	$ 503,082	$ 513,024	$ 980,674	$ 1,010,614
Gross profit	177,860	169,705	335,085	332,908
Operating Income (Loss)	36,822	35,473	66,864	59,047
Total other income (expense)	(5,255)	(2,778)	(10,236)	(6,942)
Income Before Income Taxes	31,567	32,695	56,628	52,105
Electricity Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenues	250,332	232,823	489,083	450,118
Gross profit	78,595	70,892	145,787	135,478
Operating Income (Loss)	17,653	20,008	34,515	30,640
Gas Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenues	138,700	150,266	262,911	289,522
Gross profit	50,272	53,483	100,776	102,060
Operating Income (Loss)	16,563	25,376	37,819	41,675
Water Operating Segment [Member]
Segment Reporting Information [Line Items]
Revenues	114,050	129,935	228,680	270,974
Gross profit	48,993	45,330	88,522	95,370
Operating Income (Loss)	16,686	14,177	25,421	32,253
Corporate Unallocated [Member]
Segment Reporting Information [Line Items]
Operating Income (Loss)	$ (14,080)	$ (24,088)	$ (30,891)	$ (45,521)